Typically, oxygenated blood flows from the heart into the legs and other extremities to feed the muscles and promote healthy muscle function. After delivering oxygen and other nutrients to the muscles, deoxygenated blood removes waste products, such as carbon dioxide, from the muscles in preparation for another cycle of muscle contractions.
Blood can flow from the extremities (e.g., legs and arms) back to the heart against the natural pull of gravity. Accordingly, a venous pump system can facilitate blood flow from the extremities back to the heart against gravity. A natural venous pump in the legs includes a series of valves and smooth muscle lining the blood vessels that propel blood towards the heart and inhibit backflow of the blood.
Under normal conditions, the venous pump system of the extremities returns blood to the heart in an efficient fashion. However, certain conditions (e.g., during exercise, post-trauma, surgery, other medical conditions, etc.) can cause the blood to flow less efficiently through the extremities and/or cause the muscles to require more oxygen and increased waste removal than can be supported by the body's natural circulation.
Certain devices and techniques have been proposed for improving circulation through the extremities. For instance, external devices can be used to increase circulation by cyclically compressing and releasing the extremity. For example, compression wraps having fluid-filled bladders can cyclically apply and release pressure. The bladders are cyclically inflated and deflated with use of an electric pump, etc. Other examples include systems in which discrete, fluid-filled bladders having a constant pressure are placed in various locations around a wrap or brace such that they are situated between portions of the wrap or brace and a wearer's skin to increase comfort and stability during use.